• We studied biliary excretion of sodium and chloride in 17 infants with external bile drainage through a "biliostomy" and describe four additional children who became ill from sodium depletion following external biliary drainage procedures for biliary tract anomalies. In the 17 infants, the mean ± SD bile sodium concentration was 122±15 mEq/L. The mean±SD serum sodium concentration was low (132±7 mEq/L) (normal, 138 to 145 mEq/L). The mean±SD bile volume was 388 ±317 mL/day at one year following surgery (range, 40 to 1,000 mL/day). In the four children, clinical manifestations of sodium depletion (lethargy, anorexia, dehydration, and malnutrition) necessitated hospital admission. At that time, the serum sodium concentration ranged from 109 to 129 mEq/L, and the simultaneous urinary sodium concentration ranged from 0 to 5 mEq/L. Although dietary sodium was normal, biliary losses exceeded dietary intake, resulting in salt and water depletion despite renal conservation. Children with biliary drainage procedures are at risk for sodium depletion and should be monitored closely and supplemented accordingly until biliostomy closure is performed.